Hereto known belt tensioners have a piston/cylinder unit, which comprises a cylinder and a piston arranged in its interior, and a compressed gas source, on the activation of which the piston is displaced. A belt engagement means which engages the safety belt is connected by a traction transfer means to the piston. A damping means provides for the absorption of energy on deceleration of the movement of the belt engagement means.
Tensioners for safety belts must be constructed as small as possible owing to the small space available in the vehicle. Inside or outside the cylinder, usually a damping means is provided, having a negative influence on the axial length of the tensioner, which damping means brakes the piston at the end of the tensioning way and in so doing absorbs energy, thus reducing load peaks. Owing to the length of the tensioning way and damping way necessary hitherto, known tensioners have such an axial overall length that they cannot be installed in the vehicle without a cable deflector.